* Penetration of the active agent inside the tooth. If careful preparation has been done, with leaking fillings replaced, tooth decay treated and enamel defects corrected, this option is unlikely. Penetration through the enamel is not capable of harming the body. But if the contraindications are ignored and the peroxide gets into the pulp, it can lead, at a minimum, to severe dental pain. In more severe cases, lesions of the pulp, up to its necrosis.
* Exposure of the bleaching agent to the surrounding tissues. This is quite common, but if you ignore painful sensations in the gum or mucosa area, you can get damage ranging from tissue discoloration to necrosis. Not all changes are reversible and may require long-term treatment.
* Excessive bleaching. If the wrong concentration of gel was chosen, exposure time or number of applications was exceeded, the enamel can become translucent and porous. This will give your teeth an unnatural, painful look and it will be almost impossible to get your teeth back to their former appearance.
* Hypersensitivity of the teeth. Although sensitivity is considered common and normal in whitening, in some cases it takes a hypertrophic form. Oxygen atoms trapped in the dentinal tubules cause extremely painful sensations regardless of the stimulus, and such pains may last for a long time.